1. Field of the Invention
The present invention relates to anisotropic phosphor deposition technology, and more particularly to a method and apparatus for manufacturing an auto-collimating phosphor imaging screen.
2. Brief Description of the Prior Art
In U.S. Pat. No. 4,069,355 to Lubowski et al., there is described a process for forming a phosphor screen on a patterned substrate using wide-angled vapor deposition (as in a hot-wall evaporator) so as to deposit the phosphor only on the raised portions of the substrate.
In U.S. Pat. No. 4,528,210 to Noji et al., there is described a process for sequentially depositing a multilayer input phosphor screen on a substantially smooth substrate so that individual columnar crystals of the second layer of alkali halide grow vertically upon the crystal particles of the first layer, standing close together with fine spaces therebetweensic!. A third layer is preferably deposited on the second layer as a continuous film. These three layers can be deposited by evaporating a phosphor material or materials at a prescribed temperature and degree of vacuum.
In U.S. Pat. No. 4,842,894 to Ligtenberg et al., there is described a method of manufacturing an x-ray image intensifier tube wherein a vapor deposition crucible is provided between forty and fifty degrees from the central normal to a smooth surface of a screen on which luminescent material is to be deposited. During deposition the vapor deposition source performs a circular movement about the surface to produce a layer having a regular structure and a good fill factor.
In U.S. Pat. No. 5,171,996 to Perez-Mendez, there is described a method for fabricating a particle detector of a sequence of columns of regular, controllable geometry and diameter perpendicular to the interface of luminescent material with adjacent materials wherein the columns are separated by gaps which may be evacuated or filled with air, with a light-absorbing material, or with a light-producing or light-reflective substance.
In U.S. Pat. No. 5,427,817 to Goodman et al., there is described a process for the vapor deposition of a scintillator phosphor composition with concomitant shadowing wherein the substrate is rotated through an arc relative to the vapor source of said phosphor, whereby shadowing introduces voided gaps or interstices between columns as a result of the preferential components receiving more coating flux, particularly in the presence of an oblique flux. In the present invention the limitations of the past due to the mandrel substrate fixture, in the size and quantity of applicable substrates, have been eliminated by a system scale-up that required the development of a novel, computer controlled, multi-constituent, evaporation source. Furthermore, the precise monitoring and control over material feed-rates and multiple temperature zones achieved with this source provide the means to produce more complex phosphors, as will be described in the following objects and detailed description of the invention.
While the processes of the prior art have achieved certain levels of performance, there is a desire to optimize the performance of structured, auto-collimating phosphors to achieve high ionizing radiation to quantum energy conversion efficiency and high spatial resolution.